Many compounds composed of transition metals of group 4 of the periodic table and cyclopentadienyl ligands or substituted cyclopentadienyl ligands, which are coordinating to the transition metal, have been synthesized. As well known in the prior art, these compounds are used for various organic syntheses such as catalysts for polymerization. (e.g., SYNTHESIS, Jan. 1988, 1–19 and Japanese Patent Laid-Open Publication No. S58-19309). It is disclosed that the density and molecular weight of the polymer can be changed in olefin-copolymerization by introducing substituted group into the cyclopentadienyl ligand of transition metal compound. (Japanese Patent Publication No. H7-37488, etc.)
However, most of these transition metal compounds are mono-cyclopentadienyl compounds, mono-substituted cyclopentadienyl compounds, biscyclopentadienyl compounds and bis-substituted cyclopentadienyl compounds.
There are hitherto several reports concerning triscyclopentadienyl compounds and tris-substituted cyclopentadienyl compounds. They are exemplified by Cp3ZrCl (Bul. Chem. Soc. Fr., 1978, II-292), Cp3ZrMe (Organometallics 1997, 16, 531), (MeCp)3ZrCl (Bul. Chem. Soc. Fr., 1978, II-292), (Me3SiCp)3ZrCl (Acta. Cryst., 1995, C51, 10) and Ind3MCl (M=Zr, Hf) (J. Organomet. Chem., 1997, 544, 139). The number of information of this kind is not large.
Concerning the triscyclopentadienyl metal hydride compounds and tris-substituted cyclopentadienyl metal hydride compounds (the metal is a transition metal of group 4 of the periodic table), only CP3ZrH has been hitherto reported. (The structural analyses by IR spectrometry and Raman spectrometry are reported in J. Organomet. Chem., 1982, 235, 69 and the structural analysis by X-ray diffractiometry is reported in Organometallics, 1999, 18, 3170.) Concerning the method for synthesizing these compounds, only the reactions of LiAlH4 with Cp4Zr and t-BuLi with Cp4Zr are known. In addition to these reactions, the reaction of LiAlH4 with Cp3ZrCl and the reaction of alkyl lithium with CP3ZrCl are considered. However, intended compounds are hardly obtained through these reactions because of the occurrence of a side-reaction to lose Cp ligand. Concerning the tetrakis-cyclopentadienyl zirconium compound which has at least one substituted cyclopentadienyl group other than cyclopentadienyl group, the report is hardly found because the repulsion by steric hindrance is largely caused to occur.
In other words, any transition metal compound having at least one-substituted cyclopentadienyl group among its three cyclopentadienyl ligands has not been known at all.
The mono-cyclopentadienyl metal compound, bis-cyclopentadienyl metal compound and triscyclopentadienyl metal compound are generally stable as halogenides such as chlorides (the metal is a transition metal of group 4 of the periodic table). The polyolefin that is polymerized in the presence of the catalyst of these compounds, contains a trace amount of halogen compound resulted from the catalyst. The polyolefin containing halogen compound, even when the amount is very small, is liable to be oxidized by heat or light rays and yellowing is caused to occur, so that antioxidant or halogen catcher is often used.
With the increasing tendency to the prevention of environmental problem in recent years, the polyolefin containing no additives such as halogen compound or antioxidant, which gives undesirable influence to human body, is largely demanded. Particularly, in the fields of food packages and medical appliances, the halogen-free or additive-free polyolefin is in great demand. As the metal compounds containing no halogen element, in which the metal is a transition metal of group 4 of the periodic table, there are exemplified by mono-cyclopentadienyl metal alkyl compound and bis-cyclopentadienyl metal alkyl compound. These compounds can be prepared from corresponding halogenides by using Grignard reagent or alkyl lithium.
Among these compounds, however, most of these compounds having hydrogen atom at β-position are not stable owing to the occurrence of release of β-hydrogen atom. Meanwhile, the compounds having no hydrogen atom at β-position, such as methylated compounds and benzyl compounds can exist as thermodynamically stable compounds because they are free from the releasing of the hydrogen atom at β-position. However, these alkyl compounds must be stored strictly in an inert gas atmosphere, because the compounds are liable to react with water or oxygen in the system to decompose even when the content of water or oxygen is very small. In order to synthesize the alkyl compound from tris-cyclopentadienyl metal halide, when the alkylation is carried out by using Grignard reagent or alkyl lithium, which is used in ordinary synthesizing method for complexes, the reaction to release one cyclopentadienyl ligand from the three ligands occurs. Accordingly, it is difficult to synthesize the alkyl compound at high yield through this method.
The present invention provides a novel transition metal compound, which has not been known yet. This novel transition metal compound can be an excellent catalyst exhibiting high polymerizing activity when it is used as a component of catalyst for olefin polymerization. The new metal compound contains no halogen element, so that the obtained polyolefin contains no halogen element. Accordingly, the amount of additives can be reduced as compared with conventional polyolefin. In addition, the polyolefin can also be used without adding any additive. The novel transition metal compound is composed of a transition metal of group 4 of the periodic table, three ligands of cyclopentadienyl derivative and one hydrogen atom. The transition metal compound of this kind has never been known. Furthermore, it has not been known either that the transition metal compound can be used as a component of catalyst for olefin polymerization.
The novel transition metal compound according to the present invention is a compound of a metal of group 4 of the periodic table having ligands of three cyclopentadienyl derivatives and one hydrogen atom, which compound contains no halogen element. The transition metal compound of this invention is more stable in relation to water and oxygen, as compared with the dialkylmetallocene of the same metal.